In direct contact steam injection heaters, steam is directly mixed with a liquid or slurry to heat the liquid or slurry. Direct contact steam injection heaters are very effective at transferring heat energy from steam to the liquid or slurry. Direct contact steam injection heaters provide rapid heat transfer with virtually no heat loss to the atmosphere, and also transfer both the latent and the available sensible heat of the steam to the liquid or slurry.
There are many sanitary applications in which steam injection heating can be useful. For instance, steam injection heaters can be used to heat water (or water mixed with additives) for cleaning purposes, to heat water in a kettle for cooking food, to heat a slurry, or to heat just about anything in a pulp. In each of these applications, a sanitary heater can encounter a wide range of liquid flows, and sometimes even a wide range of steam pressures and temperatures. It is desirable that the temperature of the heated liquid or slurry be precisely controlled even with varying liquid flows or steam pressures and temperatures. It is also desirable that the heater maintain stable liquid flow even over a wide range of flow rates.
There are strict requirements for apparatus used in sanitary applications. For instance, no threads, folds or pockets in which fluids or particulates can accumulate may be present in the apparatus. It is also desirable that the contact surfaces be self-cleaning. If manual cleaning of contact surfaces is needed, easy disassembly of the apparatus is required. The apparatus must also be self-draining when installed. One type of direct contact steam injection heater, which is disclosed in U.S. Pat. No. 4,473,512, has been used in sanitary applications. The sanitary steam injection heater disclosed in U.S. Pat. No. 4,473,512 can be easily disassembled using quick disconnect couplings or clamps, but has many intricate mechanical parts that require extensive manual cleaning.